Page 11 - ASME SMASIS 2016 Program

Symposia

independently control the magnetization by a variable other than an LEVERAGING KNOWLEDGE IN MED-TECH NITI TO ENABLE HIGH
electric current. Magnetoelectric strain coupling has emerged as a PERFORMANCE AEROSPACE ACTUATORS
promising method to lower the energy cost in operating these devices.
Previous work has yielded a proof of concept for lowering the coercivity
and the anisotropy of films (Co/Pt, CoFeB, Co/Pd) coupled to piezoelectric Jeremy Schaffer
materials (PZT/PMN-PT) under applied electric fields. Key to implementing Fort Wayne Metals Research Corporation
strain-manipulation of magnetization in ultrathin films and patterned Fort Wayne, IN
magnetic nanostructures is materials optimization for the properties
needed for integration with the strain-mediating ferroelectric material.
Recent investigations at the NIST Materials Science and Engineering Abstract
Division have focused on understanding the dynamic magnetic properties Processing experience in medical mono- and multifilament wire technolo-
of candidate magnetic thin films for composite magnetoelastic-piezoelec- gy may aid in the development of next gen solid state actuators. Every
tric composites using its suite of static and dynamic magnetic property year, more than 500,000 kilometers of binary, ternary and quaternary
characterization tools. In collaboration with researchers at UCLA, we have Ni-Ti-base alloys are delivered to patients in the form of life-altering
carried out the first broadband ferromagnetic resonance study of Gilbert medical devices. In these life-saving and enhancing applications, specific
damping and exchange stiffness in thin film Tb0.3Dy0.7Fe2 (Terfenol-D), a functional tuning is critical to acute and chronic performance. For
soft ferromagnetic material with the largest-known magnetostriction example, tuning of the grain size over a range of 30 nm to 10 microns,
(Gopman, et al. 2016). We have also developed an interface-coupled transformation targeting by multi-stage heat treatment and precipitate size
multiferroic heterostructure comprised of a Co/Ni multilayer sputtered distribution, deformation textures, and surface mechanical and chemical
directly onto a Pb[ZrxTi1-x]O3 (PZT) substrate (Gopman, et al. 2016). Co/Ni conditioning are some of the factors leveraged to achieve device
multilayers are a particularly rich system for studying strain-induced performance.
changes in magnetism due to the various parameters that depend
sensitively on the relative thicknesses of the individual Co and Ni layers: In spite of nitinol’s military origin and 40-year sustained use as an
tunable magnetostriction from opposing magnetoelastic coefficients in aerospace tubing coupler, the bulk of today’s approximately 500 ton
cubic Co and Ni; Gilbert precessional damping; saturation magnetization consumption of nitinol occurs in the medical device market. Here, the 8%
and out-of-plane magnetization anisotropy energy. By developing a strain recovery potential of this surprisingly ductile intermetallic, is formed
chemical-mechanical polishing process to mitigate the roughness in 1 mm into tubes, wires and sputter targets and built into everything from laser
thick ceramic PZT plates to below 2 nm rms, we enabled the growth of Co/ fabricated endovascular self-expanding stents to microtextile brain
Ni films with strong fcc(111) texture as determined by x-ray diffracatometry aneurysm occluders and highly flexible MEMS. This is a unique position in
for high magnetoelectric coupling via the direct interface with PZT. We will comparison to many metals used in medicine. MP35N, Ti-6Al-4V, and
discuss [Co/Ni] thickness optimization and the trade-off between 304SS for example, used in pacing leads, orthopaedic implants, and
magnetostriction, Gilbert damping and perpendicular magnetic anisotropy. vascular guidewires respectively are used in far higher volumes in sour
gas, aerospace, and consumer appliances in dramatically higher volumes.
Take Ti-6Al-4V, for instance: the burgeoning orthopaedic device market of
the 1970’s learned significant process-structure-function lessons from
Biography aerospace research. Today, and continuously since the 1990’s, groups
Daniel B. Gopman, PhD, is a staff scientist in the Material Measurement such as Boeing and NASA have actively sought to enable next gen solid
Laboratory at the National Institute of Standards and Technology. He state actuators to drive both weight-savings and systems reliability.
earned his PhD in Physics from New York University, where he performed
research on the switching properties of nanostructured spintronic devices. The results of this talk include a brief examination of the track record of
Dr. Gopman joined NIST in 2014 on a NRC postdoctoral fellowship to various alloys, forms and conditions in medical applications including
develop multiferroic heterostructures combining magnetic thin films with binary alloys from equiatomic through 51 at.% nickel. The alloys are
piezoelectric actuators. His current research focuses on the development discussed in light of tuning modes such as grain size, texture and surface
of novel magnetic devices for more effective control of magnetism at the condition that significantly impact functional device outcomes. Practical
nanoscale. Dr. Gopman is a co-organizer of the US Government Working processing variables such as cold work, stress-annealing atmospheres
Group on Magnetic Tunnel Junction technologies and a member of the and temperatures are discussed for their impact in med tech and with
American Physical Society, the IEEE Magnetics Society and the Materials respect to preliminary results in higher temperature actuation service.
Research Society. Aspects of tuning that may improve both mono- and multifilament
wire-based actuator performance, including self-biasing in rope
technology are also disclosed. Finally, some early stage wire-based
examples of medium to high temperature actuator technology, such as
cold-drawn, annealed and trained Ni-49.9Ti-20Zr in monofilament and
multifilament constructs will be presented and discussed in terms of
potential technical merit.
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